Automatic automotive transmission having 4-2 downshift sequence valve

Abstract

During D-RANGE operation under which a 4-2 downshift is required, a 4-2 downshift sequence valve is responsive to the pressure which is supplied to a friction element which is involved with the production of 3rd gear, and is maintained in a position wherein the 4th speed apply chamber of a band brake servo is maintained pressurized, until such time as the pressure in the 3rd speed friction element drops below a predetermined limit. When a manual valve is moved out of the D-RANGE position to one wherein engine braking is required, a control pressure is applied to the 4-2 sequence valve which immediately switches it to a position wherein it drains the 4th speed apply chamber irrespective of the 3rd speed pressure. At the same time an overrunning clutch control valve is supplied with the same control pressure and is moved to a position wherein an overrunning clutch is supplied with line pressure and engaged to enable engine braking.

What is claimed is: 
     
       1. In a transmission having: a first chamber means which is associated with the production of a first predetermined gear ratio,   a second chamber means which is associated with the production of a second predetermined gear ratio which is one gear ratio lower than the first predetermined one, and   a third chamber means for conditioning a first friction element to assume a condition wherein the transmission can produce engine braking, when supplied with hydraulic pressure; an arrangement comprising:   a friction element control valve for supplying hydraulic pressure to said third chamber means in response to a hydraulic pressure signal which is produced by a manual valve when said manual valve is set in a first predetermined position; and   a sequence valve which, in the absence of the hydraulic pressure signal, enables a shift which skips over a gear intermediate of the gear from which the shift is being made, and the gear to which is being made, said sequence valve being responsive, in the absence of the hydraulic pressure signal, to the pressure which is supplied to the second chamber means associated with the intermediate gear and arranged such that, when the pressure which is supplied to the second chamber means is below a predetermined level, said sequence valve shifts from a first state wherein pressure is supplied to said first chamber means, to a second state wherein the pressure which is supplied to the first chamber means is drained, said sequence valve being responsive to the presence of said hydraulic pressure signal to shift from the first state to the second state irrespective of the pressure being supplied to the second chamber means.   
     
     
       2. A transmission control arrangement comprising: an input shaft, an output shaft and a gear train operatively connecting the input and output shafts;   a first chamber means for conditioning said gear train to produce a first predetermined gear ratio, when supplied with hydraulic pressure;   a second chamber means for conditioning said gear train to produce a second predetermined gear ratio which is one gear ratio lower than the first predetermined one, when supplied with hydraulic pressure; and   a third chamber means for conditioning the gear train of said transmission to assume a condition wherein torque can be transmitted from said output shaft back through said gear train to said input shaft in a manner such that engine braking can be produced, when supplied with hydraulic pressure;   a friction element control valve for supplying hydraulic pressure to said third chamber means in response to a hydraulic pressure signal which is produced by a manual valve when set in a first predetermined position; and   a sequence valve which, in the absence of the hydraulic pressure signal, enables a shift which skips over a gear intermediate of the gear from which the shift is being made, and the gear to which is being made, said sequence valve being responsive, in the absence of the hydraulic pressure signal, to the pressure which is supplied to the second chamber means associated with the intermediate gear and arranged such that, when the pressure which is supplied to the second chamber means is below a predetermined level, said sequence valve shifts from a first state wherein pressure is supplied to said first chamber means, to a second state wherein the pressure which is supplied to the first chamber means is drained, said sequence valve being responsive to the presence of said hydraulic pressure signal to shift from the first state to the second state irrespective of the level of the pressure being supplied to the second chamber means.   
     
     
       3. A transmission control arrangement comprising: a gear train operatively arranged between input and output shafts;   a first chamber means for conditioning said gear train to produce a first predetermined gear ratio, when supplied with hydraulic pressure;   a second chamber means for conditioning said gear train to produce a second predetermined gear ratio which is one gear ratio lower than the first predetermined one, when supplied with hydraulic pressure;   a third chamber means for conditioning the gear train of said transmission to assume a condition wherein torque can be transmitted from said output shaft back through said gear train to said input shaft in a manner such that engine braking can be produced, when supplied with hydraulic pressure;   a friction element control valve for supplying hydraulic pressure to said third chamber means in response to a hydraulic pressure signal which is produced by a manual valve when set in a first predetermined position;   a shift valve, said shift valve being arranged to supply hydraulic fluid to said first chamber means through a first port when in an upshift position, said shift valve having a second port which is communicated with the first port when said shift valve assumes a downshift position; and   a sequence valve, said sequence valve having a drain port and a third port which is in communication with the second port of said shift valve, said sequence valve having a valve element which cuts off communication between the drain port and the third port when in a first position and establishes communication between the third port and the drain port when in a second position, said sequence valve having spring which biases the valve element toward said second position, said sequence valve having a first control chamber in communication with said second chamber means and a second control chamber which fluidly communicates with the manual valve and arranged to receive hydraulic pressure when the manual valve is set in the first predetermined position, said first control chamber being arranged to produce a bias which acts against the bias produced by the spring, said sequence valve being arranged to shift to said second position when hydraulic pressure is supplied into the second control chamber irrespective of the pressure in the first control chamber.